Debt (Details) (USD $)	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Debt Instrument [Line Items]
Debt	$ 78,832,000,000	$ 73,234,000,000
Weighted average contractual interest rate	1.43%	1.70%
Increase (decrease) in carrying value adjustment on debt	(257,000,000)
Debt maturity dates	As of March 31, 2013, our notes and loans payable mature on various dates through fiscal 2047.
Commercial paper [Member]
Debt Instrument [Line Items]
Debt	24,590,000,000	21,247,000,000
Weighted average contractual interest rate	0.24%	0.38%
Commercial paper average remaining maturity	As of March 31, 2013, our commercial paper had a weighted average remaining maturity of 84 days.
Unsecured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt	46,707,000,000	41,415,000,000
Weighted average contractual interest rate	2.19%	2.63%
Debt denominated in foreign currency	13,200,000,000	15,800,000,000
Unsecured notes and loans payable [Member] | Floating rate [Member]
Debt Instrument [Line Items]
Debt	16,800,000,000	16,700,000,000
Contractual interest rate, minimum	0.00%	0.00%
Contractual interest rate, maximum	6.00%	6.00%
Unsecured notes and loans payable [Member] | Fixed rate [Member]
Debt Instrument [Line Items]
Debt	30,400,000,000	25,500,000,000
Contractual interest rate, minimum	0.50%	0.50%
Contractual interest rate, maximum	9.40%	9.40%
Secured notes and loans payable [Member]
Debt Instrument [Line Items]
Debt	7,009,000,000	9,789,000,000
Weighted average contractual interest rate	0.60%	0.67%
Secured notes and loans payable [Member] | Floating rate [Member]
Debt Instrument [Line Items]
Contractual interest rate, minimum	0.40%	0.50%
Contractual interest rate, maximum	1.90%	1.90%
Secured notes and loans payable [Member] | Fixed rate [Member]
Debt Instrument [Line Items]
Contractual interest rate, minimum	0.40%	0.50%
Contractual interest rate, maximum	1.90%	1.90%
Carrying value adjustment [Member]
Debt Instrument [Line Items]
Debt	$ 526,000,000	$ 783,000,000